The present invention relates to an organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability, a composite, production processes therefor and uses thereof.
In organic, inorganic and metallic base materials, materials having characteristics which can not be achieved by a single material can be produced by compounding thereof, and it is just an ordinary method in development of materials in these days. For example, a fiber-reinforced plastic material (FRP) obtained by compounding a glass fiber with a polymer has a strength which can not be achieved only by the polymer alone. On the other hand, observing this material from a glass fiber side, we can take a viewpoint that a glass fiber which is fragile and has poor processability in itself is turned into a material having moldability by compounding with a polymer. Thus, compounding makes it possible to allow functions and performances which can not be achieved by a single material to be revealed by making the best use of the characteristics of the respective base materials or making up the defects thereof. In conventional compounded materials, a size of a disparate material (dispersed phase) in a matrix (dispersion medium) is of an order of micrometer or larger, and effects expected from compounding in such a size have been brought.
It has come to be reported in many cases that microminiaturization of a dispersed phase of a compounded material into a nanometer order in combination with an advance in a technique to analyze a micro area represented by a scanning probe microscope (SPM) makes it possible to prepare materials having a high function and multifunctions or materials having a new function which have not been able to be achieved by conventional compounded materials, and attentions are paid thereto.
Known as examples of materials (hereinafter referred to as a nano-composite) obtained by compounding organic materials with inorganic materials in a nanometer order are nano-composites obtained by compounding stratified clay minerals such as clay and synthetic stratified silicates with polymers such as nylon and nano-composites of silica with polymers making use of a sol-gel method. In the former nano-composites, investigates are (1) a method of inserting an organic monomer between layers of a stratified compound to carry out polymerization, (2) an in-situ polymerization method of carrying out polymerization of a polymer and production and dispersion of a filler at the same time and (3) a method of carrying out mixing and dispersing a stratified compound and a polymer in the presence of an organic cation. These methods make use basically of a cleavage phenomenon of a filler following intercalation of an organic substance, so that an inorganic substance is restricted to a stratified clay mineral which can be dispersed as a structure of a nanometer order. In the latter nano-composites, nano-compounding an inorganic substance with an organic substance has become possible by synthesizing the inorganic substance at a low temperature by a sol-gel method. They have the merit that refined inorganic raw materials can be used but have the defects that the raw materials are expensive and the volume shrinks as the reaction goes on.
In a nano-composite of an organic polymer with an inorganic substance, worked out as well in addition to an intercalation method and a sol-gel method is a method in which an inorganic substance is mechanically pulverized into a nanometer order and then mixed with an organic polymer to obtain an organic-inorganic nano-composite. In general, however, it is recognized that it is difficult to mechanically pulverize an inorganic substance into a nanometer order, and even though can be pulverized, it is not easy to mix homogeneously with an organic polymer which is a disparate material in a nanometer order while inhibiting recoagulation.
The present inventors have paid attentions to that if used as a component for an organic-inorganic nano-composite are calcium phosphates such as hydroxyapatite (hereinafter abbreviated as HAp) and tricalcium phosphate (hereinafter abbreviated as TCP), which are not biologically toxic and have high affinity with an organic substance, there is a possibility they may be turned into very useful materials. HAp is an inorganic component constituting a hard tissue of a vertebrate, and researched is practical use thereof as a hard tissue-substituting material for an artificial bone, an artificial root of tooth and an artificial joint. An HAp sintered substance is a brittle material which is strong against compression but weak against tension if it is used alone, and it has the defect that the moldability is poor. Disclosed as a method for improving this defect in Japanese Patent Application Laid-Open No. Hei 10-229 is a technique for obtaining an organic-inorganic composite which is improved in stability in molding processing and well balanced in flexibility, strength, an elastic modulus, reproducibility and molding processability by mixing HAp with lactic acid base polyesters. This technique has been developed based on an idea to provide a material closer to an organism considering that HAp is present in an organism in the form of a compounded product with collagen which is a biopolymer. In this method, a composite is obtained by synthesizing a calcium phosphate compound such as HAp or TCP by a wet process, baking and pulverizing the resulting precipitate and then mixing it with a polymer by means of a mixer. Calcium phosphate particles used in this case have a size of 5 mm or less, and the organic polymer is restricted to a lactic acid base polyester. This material has achieved osteoconductivity and biocompatibility making the best use of the characteristics of the respective base materials, and it is not a material which is homogeneously dispersed in a nanometer order.
On the other hand, according to Japanese Patent Application Laid-Open No. Hei 7-101708, disclosed is a composite which comprises HAp powder having a crystal particle diameter of 0.5 xcexcm (500 nm) or less and an organic substance such as collagen and which is close to a tooth and a bone of an organism. In this technique, obtained is a composite having a high Young""s modulus by adding a mixed solution of collagen and phosphoric acid to a suspension of calcium hydroxide while vigorously stirring, filtering and drying the resulting precipitate to obtain a hydrate and applying a pressure of 200 MPa to the hydrate at 40xc2x0 C. It is confirmed by Tanaka et al. [BIO INDUSATRY, Vol. 13 (No. 8), 28 (1996)] that this HAp-collagen composite is a nano-composite in which C axis of HAp nanocrystals (some nm) is orientated along collagen fibers (30 nm). However, included in producing materials close to a vital bone are the problems that a synthetic method in which strength close to that of a vital bone can freely be controlled has to be established and that a method of reducing antigenicity of collagen has to be established. Further, this material is not a material having a high transparency which is characteristic to a nano-composite since it has an oriented structure.
Inorganic substances such as calcium phosphate and calcium carbonate which can be synthesized by a liquid phase process are liable to be turned into a low crystalline substance or a fine crystal in many cases, and they are usually turned into a gelatinous precipitate. Usually, used is a material obtained by filtering, drying, baking and then pulverizing this precipitate, but it is difficult to pulverize them to a primary particle, and it is not easy as well to disperse and mix nano-order particles in a polymer. Thus, a practical method of producing a composite in which an inorganic substance including calcium phosphate synthesized by a liquid phase process is homogeneously dispersed in a nano order has not been available in conventional techniques.
The paper-making industry is an industry in which a large quantity of forest resources is consumed as raw materials and a great amount of energy is required for producting pulp and in a paper-making step, and in the state that environment problems become more serious on a global level in recent years, an effort toward reducing a load onto the environment as much as possible is energetically made. In particular, recycling of waste paper as resources increases the importance further more, and it is said that recycling goes on up to a level close to a limit excluding unrecoverable paper such as sanitary paper and paper for books. However, waste paper is a raw material in which fibers are shortened by cutting and abrasion, and therefore an elevated use ratio thereof results in bringing about a reduction in strength of the paper. Such reduction in paper strength has been made up by adding or coating a water-soluble high molecular compound represented by starches such as starch oxide and cationized starch, polyvinyl alcohol (PVA) and (meth)acrylamide base polymers. On the other hand, paper-strengthening agents comprising the water-soluble high molecular compounds described above are used in order to make up a reduction in paper strength also when adding various additives which are mainly inorganic pigments for the purpose of reducing a use amount of pulp from a viewpoint of resource saving.
Among those paper-strengthening agents, the (meth)acrylamide base polymers are known as a high performance chemical which brings about a large effect by a trace amount. However, environmental problems are important subjects which have to be now considered in a global scale, and chemicals having higher performances than ever have increasingly been desired to cope with the problems of deteriorating in the quality of raw materials and reducing the amount of pulp.
There have so far been investigated as a method of providing a (meth)acrylamide base polymer with a high paper-strengthening ability, a method in which it is copolymerized with a functional monomer, a method in which a functional group is introduced thereinto by after-modification and a method in which a cross-linking structure is introduced thereinto. However, in the state that the further higher performances are required in the future, the performances which can be achieved only by conventional methods of modifying polymers are limited, and therefore chemicals for paper making based on a new concept are desired to be provided.
Printing by an ink jet recording system has the advantages that it has less noise and is silent; high-speed printing is possible; a printing cost is low; coloring is easy; printed record is clear; and printing in a large size is possible. Accordingly, it prevails widely. The ink jet recording system is a recording system in which ink droplets are jetted from fine nozzles by various operating methods and adhered on a recording sheet such as paper to obtain information in the form of a letter or an image. Required to the sheet used for the ink jet recording system are such characteristics that the droplets adhered on the sheet surface according to the principle of the above system are quickly absorbed into the sheet and that spreading and feathering on the surface are controlled and the ink stays in the vicinity of the sheet surface as much as possible in order to elevate the color-developing intensity.
It has so far been proposed as a method of endowing an ink jet recording sheet with these characteristics to provide an ink absorptive coating layer on a sheet surface. Proposed is, for example, a coating layer comprising silica powder or alumina powder having high absorptivity and a binder of a water-soluble polymer such as polyvinyl alcohol as principal components and further comprising various additives mixed in order to improve an ink-fixing property and water resistance.
Thus, an ink jet recording sheet having a coating layer using silica powder or alumina powder as an inorganic filler is improved in ink absorptivity to a large extent and makes it possible to obtain an image having high image quality. However, brought about is the defect regarding the light fastness that the above coating layer is discolored to a yellow color with storing over a long period of time. In recent years, an outstanding progress in an ink jet printer has made it possible to readily obtain an image having high image quality in full colors. A recording sheet therefor has to have high whiteness, and therefore the preceding defect regarding light fastness such as yellowing with the passage of time is a large problem. Further, a recording sheet having the above coating layer has the problem that a part on which an adhesive tape is stuck causes marked yellowing when the adhesive tape is stuck on it. Thus, there has been involved the defect that when an adhesive tape is stuck on the above recording sheet for fastening, the appearance is notably damaged by yellowing.
The present inventors considered that if developed is a material which does not produce precipitates in the course of compounding calcium phosphate including the HAp described above and other inorganic substances with a polymer and which can be turned into a molded article without applying high pressure, it will be a material which is useful in many fields such as paper-making chemicals as well as vital materials. However, in nano-compounding with a polymer, there are inorganic substances to which a compounding method by the intercalation method and the sol-gel method each described above can not be applied. Accordingly, the present inventors have paid attentions to that some of inorganic substances can be synthesized in an aqueous medium by a liquid phase process other than the sol-gel method, and they have come to consider that those inorganic substances may be able to be nano-compounded with water-soluble or water-dispersible polymers.
An object of the present invention is to provide an organic polymer/inorganic fine particle-dispersed aqueous solution which has excellent molding processability and forms a transparent film and which can be used for various uses by stably dispersing inorganic nanometer-order fine particles without causing coagulation with and separation from water-soluble or water-dispersible polymers, which has so far been difficult in conventional methods, and uses thereof.
The present inventors have found that a composite obtained by combining a water-soluble or water-dispersible synthetic high molecular compound having a carboxyl group with a water slightly soluble inorganic particle having a particle diameter of 500 nm or less, particularly a water slightly soluble inorganic particle having a particle diameter of 500 nm or less obtained by reacting a compound of a second group element in the periodic table with at least one compound selected from organic acids, inorganic acids and salts thereof is a material which meets the object described above, and the present invention has come to be achieved.
That is, the present invention comprises:
(1) an organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability comprising a water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group and a water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less in a proportion of (A):(B)=10:90 to 99.99:0.01 (weight ratio),
(2) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in the above item (1), wherein the water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less is a fine particle of a compound of a second group element in the periodic table,
(3) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in the above item (1), wherein the water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less is synthesized by reacting (a) a compound of a second group element in the periodic table with (b) at least one compound selected from organic acids, inorganic acids and salts thereof in the presence of the water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group,
(4) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in the above item (3), wherein (b) the organic acid or inorganic acid is at least one acid selected from oxo-acids and hydrohalogenic acids,
(5) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in the above item (3), wherein (a) the compound of a second group element in the periodic table is a calcium compound,
(6) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in the above item (3), wherein the water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group is a polymer of an ethylenically unsaturated compound,
(7) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in the above item (6), wherein the polymer of the ethylenically unsaturated compound is any of a (meth)acrylamide base polymer, a carboxyl group-modified polyvinyl alcohol and a vinylpyrrolidone base polymer,
(8) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in the above item (6), wherein the the polymer of the ethylenically unsaturated compound is any of:
{circle around (1)} (meth)acrylamide base polymer which is a polymer of 1 to 100% by weight of an ethylenically unsaturated carboxylic acid amide compound and 0 to 99% by weight of a copolymerizable, ethylenically unsaturated compound,
{circle around (2)} a carboxyl group-modified polyvinyl alcohol which is produced by saponifying a polymer of an ethylenically unsaturated carboxylic acid and vinyl acetate, and
{circle around (3)} a vinylpyrrolidone base polymer which is a polymer of 1 to 99.9% by weight of N-vinyl-2-pyrrolidone and 0.1 to 99% by weight of a copolymerizable, ethylenically unsaturated compound,
(9) the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in any of the above items (6) to (8), wherein the water slightly soluble inorganic fine particle (B) is calcium phosphate,
(10) a production process for an organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability, characterized by producing a water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less by reacting (a) a compound of a second group element in the periodic table with (b) at least one compound selected from organic acids, inorganic acids and salts thereof in the presence of a water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group,
(11) an organic polymer/inorganic fine particle-composite having excellent transparency comprising a water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group and a water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less obtained by reacting (a) a compound of a second group element in the periodic table with (b) at least one compound selected from organic acids, inorganic acids and salts thereof in a proportion of (A):(B)=10:90 to 99.99:0.01 (weight ratio),
(12) an organic polymer/inorganic fine particle-composite having excellent transparency obtained from the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in any of the above items (1) to (9), comprising a water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group and a water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less in a proportion of (A):(B)=10:90 to 99.99:0.01 (weight ratio),
(13) the organic polymer/inorganic fine particle-composite having excellent transparency as described in the above item (11) or (12), wherein the composite is a film having excellent transparency,
(14) the organic polymer/inorganic fine particle-composite having excellent transparency as described in the above item (11), wherein the water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group is any of a (meth)acrylamide base polymer, a carboxyl group-modified polyvinyl alcohol and a vinylpyrrolidone base polymer.
(15) The organic polymer/inorganic fine particle-composite having excellent transparency as described in the above item (11) or (14), wherein the water slightly soluble inorganic fine particle (B) is calcium phosphate,
(16) a paper-making chemical comprising a water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group and a water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less obtained by reacting (a) a compound of a second group element in the periodic table with (b) at least one compound selected from organic acids, inorganic acids and salts thereof in a proportion of (A):(B)=10:90 to 99.99:0.01 (weight ratio),
(17) a paper-making chemical obtained from the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in any of the above items (1) to (9),
(18) a chemical for an ink-jet recording sheet comprising a water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group and a water slightly soluble inorganic fine particle (B) having a particle diameter of 500 nm or less obtained by reacting (a) a compound of a second group element in the periodic table with (b) at least one compound selected from organic acids, inorganic acids and salts thereof in a proportion of (A):(B)=10:90 to 99.99:0.01 (weight ratio),
(19) a chemical for an ink-jet recording sheet obtained from the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in any of the above items (1) to (9),
(20) the chemical as described in the above item (16) or (18), wherein the water-soluble or water-dispersible synthetic high molecular compound (A) having a carboxyl group is any of a (meth)acrylamide base polymer, a carboxyl group-modified polyvinyl alcohol and a vinylpyrrolidone base polymer,
(21) the chemical as described in the above item (16) or (18), wherein the water slightly soluble inorganic fine particle (B) is calcium phosphate,
(22) paper obtained by using the chemical as described in any of the above items (16) to (21),
(23) a cosmetic comprising the organic polymer/inorganic fine particle-dispersed aqueous solution having excellent dispersion stability as described in any of the above items (1) to (9), and
(24) a cosmetic comprising the organic polymer/inorganic fine particle-composite having excellent transparency as described in any of the above items (11) to (15).